Most common wire is 22ga, 600v if I remember correctly. Some 18ga and 22ga buss wires.
The 12xxx does not have an instruction. There is a lot of work gathering all the information you will need. You will feel overwhelmed. Without a complete kit that feeling will be multiplied. Because you have a search for components running in the back.
I would probably have started on populating the boards after the initial wires are done. The boards can then be stored for later.
What I would suggest is that you start reading the forum.
1) Searching for "12xxx build", "12xxx pictures", "12xxx step by step" and so on.
2) Go to Wiki - Amp instructions, and download all instructions. This will be your bed-literature the next weeks. And none are really your build

The reason I still recommend it is that they all have parts that you may take with you. And you get a feeling for how it is done.
3) You need layouts. Some are found on the CD that comes with the barebone kit. And
SDM has one (even though it does not have the same power section as your build will have; it is absolute GREAT for 12xxx).
http://home.comcast.net/~jbjdav26/1959/ ... 0grids.JPG" onclick="window.open(this.href);return false;
You may also like the rest of his site; great one
http://home.comcast.net/~mamp17/index.html" onclick="window.open(this.href);return false;
4) With all this digested take a new look at what vkaxeman ended up with
http://forum.metroamp.com/viewtopic.php ... &start=705" onclick="window.open(this.href);return false;
And take notice as how the tone was achived by reading the thread...a LOT of pages (I never got through them all...). I think he was slaving amps for that sound. That means another amp
It is a long walk. And will cost.
So what would I do?
Just get the barebone plus wires and tube sockets. And worry not for the struggle up ahead. Small steps.